Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Since then, large efforts have been spent to grow carbon fibers with diameters in the
nanometer range (50–200 nm) in the vapor phase by catalytic decomposition of
hydrocarbons [17, 76]. Currently, Applied Sciences Inc (ASI, Cedarville, Ohio, USA)
produces VGCFs denoted as Pyrograf III of different types, namely PR-1, PR-11,
PR-19 and PR-24 [77, 78]. The PR-1, PR-11, and PR-19 nanofibers are 100–200 nm in
diameter and 30–100 mm in length. The PR-24 fibers are 60–150 nm in length and
30–100 mm long [77]. Pyrograf III fibers find widespread application as reinforcement
materials for polymer composites [6]. In Europe, VGCFs are also commercially
available from Electrovac Company [79, 80]. These nanofibers include ENF100 AA
(diameter of 80–150 nm), HTF110FF (diameter of 70–150 nm) and HTF150FF
(diameter of 100–200 nm); these fibers are longer than 20 mm.
Satishkumar et al. [81] and Jang et al. [82] synthesized CNTs by pyrolysis of iron
pentacarbonyl [Fe(CO) 5] with methane, acetylene or butane. Ferrocene with a
sublimation temperature of 140 C is widely recognized to be an excellent precursor
for forming Fe catalyst particles. Figure 1.11 is a schematic diagram showing
a typical pyrolysis apparatus for the synthesis of CNTs. Ferrocene is placed in the
first furnace heated to 350 C under flowing argon. The ferrocene vapor is carried
by the argon gas into the second furnace maintained at 1100 C. Hydrocarbon gas is
finally introduced into the pyrolysis zone of the second furnace. The pyrolysis
of ferrocene–hydrocarbon mixture yields iron nanoparticles. After the reaction,
carbon deposits are accumulated at the wall of a quartz tube near the inlet end
of the second furnace. Rohmund et al. used a single-step, single furnace for the
catalytic decomposition of C 2H 2 by ferrocene [83]. In some cases, MWNTs can be
produced by pyrolyzing homogeneously dispersed aerosols generated from a solution
containing both the hydrocarbon Source (xylene or benzene) and ferrocene [84].
Andrews et al. reported that large quantities of vertically aligned MWNTs can be
produced through the catalytic decomposition of a ferrocene–xylene mixture at
Figure 1.11 Schematic layout of a processing system designed for
the synthesis of aligned CNTs by the pyrolysis of ferrocene–
hydrocarbon mixtures. Reproduced with permission from [81].
Copyright Ó (1999) Elsevier.
1.3 Synthesis of Carbon Nanotubesj15